A numerical control device mounted on a machine tool always monitors occurrence of an abnormality in the operation and the state of the machine tool. Upon detecting occurrence of an abnormality, the numerical control device raises a warning (an alarm) with display, sound, or the like and stops driving of the machine tool. By stopping the driving of the machine tool, the numerical control device prevents malfunction of the machine tool and breakage of the machine tool or the like due to the malfunction.
The abnormality of the machine tool is caused by various factors. The factors of the abnormality are that, for example, a driving load of a motor becomes excessively large because of a lubrication failure, a cutting load becomes excessively large because of breakage of a tool, and an error between a command position and a motor detection position becomes excessively large. As the alarm, besides an alarm due to an event that could regularly occur, an alarm due to an irregular event with low reproducibility is also present such that, for example, an alarm is raised according to a state of removal of chips.
When an alarm is raised in the machine tool, after content of the alarm is checked, recovery work for eliminating a factor causing the alarm is carried out. When the recovery work is finished, the machine tool resumes machining. Usually, a user, a maintenance staff member, or the like performs the check of the content of the alarm and the recovery work.
The recovery work can be sometimes automatically carried out without human intervention. For example, Patent Literature 1 proposes a numerical control device that enables automatic recovery of a machine tool using a recovery operation program corresponding to content of an abnormality. Patent Literature 2 proposes a control method for automatically generating, when an automatic operation by an NC program command is suspended, a recovery procedure according to content of an operation executed according to the NC program command.
If automation of the recovery work is possible, it is possible to reduce time required for recovery and labor for the recovery. Even if machining of work is suspended because an alarm is raised, the machine tool can resume the following machining of the work early without human intervention.